THURSDAY, Aug. 15 (HealthDay News) -- If you decide to hit the gym in hopes that a quick dose of exercise will cure your insomnia, a new study suggests that will not be enough.

While adopting an exercise program did ultimately help some insomniacs sleep better, the scientists found the impact was far from immediate.

"Where the idea to explore this came from is that my patients were coming in and saying that they heard that exercise is good for sleep," explained study author Kelly Baron, director of the Behavioral Sleep Medicine Program with the Feinberg School of Medicine at Northwestern University in Chicago. "But people generally want a quick fix. And they weren't seeing improvements right way. So, they were getting discouraged," she said.

"The message here is that exercise is not a quick fix, which I don't really think is discouraging at all," Baron said. "Our previous work found that exercise over a 16-week period is very effective in promoting sleep, on par with any kind of medication. But like with weight loss or any sort of behavioral change, it doesn't happen immediately. You have to measure progress over months, not day-to-day."

Baron and her colleagues published their latest findings online Aug. 15 in the Journal of Clinical Sleep Medicine.

With this latest study, the dashed expectations came after the researchers took a closer look at earlier data on the sleep habits of 11 sedentary middle-aged and elderly women. All had been diagnosed with insomnia before beginning a four-month, monitored regimen of aerobics.

By the end of the four months, the exercise regimen did help boost sleep, mood and vitality among older women with insomnia who had not previously exercised.

All of the women had kept track of their sleeping patterns using sleep logs, both before starting to exercise and four months into their new routine. All were outfitted with wristwatch monitors that kept a record of activity rhythms during sleep.

The result of the new look at the numbers: A single exercise session during the day did not help promote improved sleep that same night.

Not only that, a reverse relationship was noted, in which sleeping poorly one night led to a decrease in the amount of time a person spent exercising the next day. This meant that the insomniacs were at risk of falling into a vicious cycle, in which they ended up being too tired to exercise regularly to get better sleep in the long term.

"So, what this means is that patients need to plan ahead," Baron advised. "They need to schedule exercise. Make it premeditated and part of one's routine, especially on those days when they feel tired or fatigued or didn't sleep well, because even if the sleep benefit doesn't come quickly, with time and commitment it may eventually come."

However, Dr. James Pagel, director of the Sleep Disorders Center of Southern Colorado in Pueblo, sounded a cautious note on the findings, because "insomnia is not the same for everyone."

"Here they were looking at how exercise could specifically benefit primarily elderly women with insomnia who didn't exercise beforehand," he noted. "But there are at least 60 different diagnoses associated with insomnia. And 14 percent of the American population has chronic insomnia. So, it's a big group of people, and it's very diverse," Pagel said.

"So, yes, there was a long-term, if not short-term, benefit for this group, which I would expect we would see for many similarly aged-men as well," he noted.

"But I have a large group of patients who run marathons. I have people who are insomniac and run many miles a week. And they still can't sleep, because insomnia is an abnormality of arousal, and for some people you're not just unable to sleep, but you're also hyper-aroused during the day and often committed to a very intense exercise pattern. And for these individuals, and those with a genetic form of insomnia, for example, exhausting themselves with exercise will not induce sleep," Pagel explained.

"So, this is great news for this population that they looked at," he added. "But it won't apply to everyone."